Such a pressure filter is known from EP 0 479 077 A1. This pressure filter works with a continuous cleaning of the filter surface and is especially intended for the separation of solids from suspensions. The pressure filter comprises a plurality of pressure-tight filter elements separating the fluid compartment from the filtrate compartment and forming the filter surface while the backwashing means is connected to the reject drain and has a backwashing head sealing a part of the filter surface with respect to the fluid compartment. The backwashing head and the filter surface are movable with respect to one another. The fluid to be filtered is supplied to the pressure filter with a pressure p.sub.1 and acts on the filter elements with this pressure p.sub.1 in the fluid compartment. The filtrate is drained from the filtrate compartement with a lower pressure p.sub.2. In the reject drain and backwashing compartment, restricted by the backwashing head, a pressure p.sub.3 is adjustable which is always smaller than the pressure p.sub.2 in the filtrate compartment. A filtration occurs because of the pressure difference between the pressure p.sub.1 of the fluid compartment and the pressure p.sub.2 of the filtrate compartment, wherein solids are deposited on the filter surface and form a cover layer. This cover layer is continuously cleaned by backwashing, i.e. a conversion of the flow direction through the filter elements. The backwashing occurs at that portion of the filter surface which is sealed by the backwashing head with respect to the fluid compartment with a pressure difference between the pressure p.sub.2 in the filtrate compartment and the pressure p.sub.3 in the backwashing compartment. The filtration process at the remaining filter surface of the pressure filter is not influenced by the backwashing.
In the known pressure filter the backwashing compartment has at least one suction chamber open to the filter surface in a slot-like manner. This suction chamber is formed as elongated chamber extending from a central drive shaft for the backwashing head radially outwardly. Upon rotation of the backwashing head the slot-like aperture sweeps over the filter surface as a radial beam emanating from the center of the pressure filter.
In detail, the known pressure filter has a plurality of filter-carrying filter plates which are stationary in a pressure container. The backwashing heads disposed on a hollow shaft extending through a pressure container engage into fluid spaces between the filter plates. The hollow shaft extends laterally outwardly from the pressure container and is connected there to a suitable drive means. The individual backwashing heads are driven by rotation of the hollow shaft. Furthermore, the hollow shaft serves for draining the reject evacuated by means of the backwashing heads. All the backwashing heads are secured to the cylindrical portion of the hollow shaft.